Electric vehicles present a growing application for rechargeable batteries, and in particular for large battery packs. Such an application, however, presents a number of engineering challenges to the power system designer, primarily due to the need to balance the expectations of the consumer with the system requirements and the constraints placed on the system by the batteries within the battery pack. Consumer expectations include those associated with the vehicle as a whole, e.g., vehicle range, performance and reliability, and those that are specific to the vehicle's battery system, e.g., battery pack lifetime and replacement cost, and the time, cost and convenience associated with charging the vehicle. System requirements include power output, battery pack weight and reliability. Battery constraints include those associated with charging, operational, and storage temperatures; charge rates; the level of allowed/preferred charging (i.e., 75% of full charge, full charge, over-charged, etc.); and the level of discharge allowed before charging.
To address some of the issues associated with batteries, sophisticated charging algorithms may be employed. For example, co-pending U.S. patent application Ser. No. 12/322,217 discloses a system for controlling the charging system of an electric vehicle, more specifically the charging level, based on a number of parameters. Disclosed parameters include expected travel distance, road conditions, weather conditions, desired battery power safety margins and driving style. Co-pending U.S. patent application Ser. No. 11/779,837 discloses an alternate charging system controller that determines the optimal time to charge a battery pack based on charging cost, thus taking into account variations in the cost of electricity based on the time of day. Co-pending U.S. patent application Ser. Nos. 12/321,279 and 12/322,219 disclose an alternate charging system controller that determines the optimal cut-off voltage to be used during charging based on desired vehicle performance, driving range, vehicle usage and battery life.
While the prior art charging system controllers may take into account a variety of factors in determining optimal charge rates, charge levels, and charging times, these systems do not control the loads placed on the batteries during charging, for example those associated with auxiliary cooling systems. As a result, these system controllers do not effectively optimize battery pack charging time. Accordingly, what is needed is a system controller that can control both the charging system and any auxiliary loads placed on the batteries during charging, thus allowing the charge time to be optimized for a particular situation. The present invention provides such a system.